Apple's late-October launch of Leopard generated the best first-month results for an operating system upgrade in the company's history, a market research firm said Monday.

Just days before Leopard's 26 October debut, Chris Swenson, an analyst at NPD Group, wondered whether it could beat the extraordinary performance of Tiger. "It's going to be really hard to top the Tiger launch," he said then. "It was such a successful launch."

Monday, however, Swenson said that Leopard bested Tiger in almost every sales category.

According to NPD's data, unit sales of Leopard, formally known as Mac OS X 10.5, were up 20.5% over predecessor Tiger's, when both versions' first-month numbers were compared. Leopard's revenue was up even more: 32.8% higher than Tiger's.

NPD, which pulls its numbers primarily from brick-and-mortar retailers but also from a smattering of online sellers – including Apple's online store and Amazon.com – separated the boxed copies of Leopard from any sold preinstalled on new Macs, just as it did with Tiger and the edition before that, dubbed Panther. Apple, on the other hand, included every possible copy of Leopard when it touted sales of two million during the operating system's first weekend.

As Swenson predicted in October, the biggest contributing factor to Leopard's success was the larger number of Apple-owned retail stores selling the product. Apple now has about double the number of stores compared with its line-up in May 2005, when Tiger launched.

The time of year also played a part. "They're moving a lot of volume through their stores," said Swenson. "I guess there's something to be said for pushy sales reps talking up the operating system."

Other factors, however, helped Leopard's sales, including the month. November, Swenson said, is a "key month for consumer shopping," unlike May, Tiger's first month of sales.

But additional stores and the season can't explain all of Leopard's success. "It's clear that Apple has hit upon the right strategy for rolling out new versions of its OS," Swenson said.

The boost in revenue, on the other hand, has different parents.

Some of the increase can be attributed to the bigger slice of total sales that Apple's Family Pack took. Nearly a third (32.8%) of all Leopard units tracked by NPD were the five-licence Family Pack, a major bump from the 20.4% of Tiger's sales. Not surprisingly, that drove up the average sales price of Leopard to US$144.30 in its first month, compared with Tiger's first-month average of $128.50. (The two upgrades were priced identically: $129 for a single license, and $199 for the Family Pack.)

"That's one that I was bearish on," Swenson admitted. "I wondered [before Leopard's launch], 'How many more can they sell?' Well, Apple was obviously able to continue to grow that."

Also contributing to the growth in average sales price was the apparently smaller number of retailers offering substantial rebates or discounts on the operating system during the launch, said Swenson. "Amazon, for example, was doing some crazy sales with Tiger, but there really weren't any fire sale prices or big rebates for Leopard," he noted.

The only Tiger record that Leopard didn't break was the former's mark for the biggest percentage increase from one release to the next. Tiger, for example, sold approximately 30% more units in its first month than its immediate predecessor, 10.3, a.k.a. Panther.

"Personally, I thought these numbers were surprising," concluded Swenson, who also contrasted Leopard's opening with Microsoft's first month selling Windows Vista earlier in 2007. "Vista was a much more radical jump [than Leopard] on its hardware requirements, which meant smaller percentages of users upgrading old machines.

"Microsoft has experienced launches like this before," he said. "Windows ME is a good example. But Apple has yet to stumble. It's really stunning to see Apple have one blowout OS launch after another."

Apple won't report on the quarter from which NPD drew its numbers until late January; the current quarter will close 31 December.